Surface plasmon resonance sensing: an optical fibre based SPR platform with scattered light interrogation

This thesis describes the development, fabrication and optimisation of a Surface Plasmon Resonance (SPR) sensing architecture based on optical fibres. Motivated by biosensing applications, SPR was chosen as a simple and sensitive label-free technique that allows real time quantitative measurements of biomolecular interactions. Unlike conventional fibre SPR probes, this platform utilises a novel interrogation mechanism based on the analysis of scattered radiation facilitated by a rough plasmonic coating. A theoretical study is performed in order to determine the optimal parameters of the sensing configuration, i. e. the metal coating and fibre material. This analysis revealed a trade-off between the sensitivity of these devices, and their resolution. Optical fibres with cores made of lower refractive index materials were found to increase the sensitivity of the sensor, but broaden the SPR spectral signature. This broadening of the linewidth results in an unwanted increase in the sensor resolution, which leads to an undesirable increase in the detection limit. Therefore, experiments were performed to investigate the trade off between the sensitivity and resolution of the sensor to optimise both performance characteristics. The experimental demonstration and characterisation of a scattering SPR platform based on lead silicate fibres is described. The plasmonic coating with required surface roughness was fabricated using chemical electroless plating. In order to increase the refractive index sensitivity, a fibre SPR sensor with a lower refractive index core made of fused silica was produced. Due to the different surface properties of the silica glass and the lead silicate glass, surface modification with stannous chloride was required to fabricate suitable plasmonic coatings on the fused silica fibres. Characterisation of the new fused silica SPR sensors showed that the sensitivity of the sensing probe was improved, however, the spectral linewidth of the SPR signature was broadened, in agreement with the theoretical modelling. Nevertheless, analysis of the capability of the silica fibre based SPR sensors demonstrated potential for this platform in biological studies. To improve the resolution without affecting the sensitivity of a sensor, smaller core fibres can be used. However, using conventional small core fibres or fibre tapers is challenging due to their fragility and the requirement for fibre post processing to access the core. To overcome these difficulties, an SPR sensor based on a silica microstructured optical fibre with a core exposed along the entire fibre length was fabricated. Exposed Core Fibres (ECFs) have small cores that are supported by thin struts inside of a larger support structure, providing mechanical robustness to the fibre. The ECF SPR sensing platform doubled the improvement in the spectral linewidth when compared to the large core fused silica fibre sensor, without compromising sensitivity. Finally, the demonstration of Metal Enhanced Fluorescence (MEF) phenomena is presented. The effect of rough metallic coatings on the enhancement of fluorescence emission is investigated in planar glass substrates, showing significant improvement in emission when compared to smooth metal films. An optical fibre based MEF platform was demonstrated to illustrate the potential of rough metal coatings on a fibre for surface enhanced optical phenomena. This work is the first systematic study of a scattering based SPR sensing platform. This architecture addresses existing practical limitations associated with current SPR technologies, including but not limited to bulk design and affordability. Additionally, performance enhancement of the sensing probes is achieved through the use of alternative fibre material and geometry. The demonstrated performance improvements are not class-leading compared to commercial biosensing devices, however, the performance is in agreement with the theoretical analysis which provides a pathway for further improvement. This demonstrated that the scattering based SPR fibre platform is a practical new approach that offers the advantages of high sensitivity and signal to noise ratio, and low resolution, with the capability to improve the detection limit of SPR devices. Most importantly, this novel SPR interrogation approach allows the incorporation of two different sensing techniques, SPR and fluorescence, in the same fibre device, which opens pathways for novel biosensing applications combining the two phenomena.Thesis (Ph.D.)--University of Adelaide, School of Physical Sciences, 2017

Investigation of a SPR based refractive index sensor using a single mode fiber with a large D shaped microfluidic channel

In this work, a highly sensitive surface plasmon resonance (SPR) sensor based on a single mode fiber (SMF) incorporating a large microfluidic channel (MFC) for refractive index (RI) sensing is designed and optimized using a full-vectorial finite element method (FEM). The fluidic channel size can be varied according to the requirement due to the availability of the large cladding diameter of SMF, which makes it simple and easy to fabricate. The proposed novel sensor is favourable to both analytes and metallic strips. The D-shaped hollow section above the core is filled with the measurand analytes and a gold (Au) strip is deposited on the base of the MFC, as it is known as the most attractive metal for SPR. Our numerical simulations illustrate that the confinement loss of the designed sensor is highly influenced by the distance of the MFC from the core along with the width and thickness of the Au strip. The designed sensor shows an average sensitivity of 1350 nm/RIU and maximum sensitivity of 8250 nm/RIU in the sensing range of 1.33-1.35 and 1.41-1.43, respectively. However, for a small variation of na at a step of 0.005, within ranges like 1.415, 1.420, and 1.425, we have achieved a maximum sensitivity of 7000 nm/RIU, 9000 nm/RIU and 11000 nm/RIU, respectively. This novel SPR sensor with MFC can open up a new opportunity in the application of chemical and biological sensing

Wavefront Curvature in Optical Atomic Beam Clocks

Atomic clocks provide a reproducible basis for our understanding of time and frequency. Recent demonstrations of compact optical clocks, employing thermal atomic beams, have achieved short-term fractional frequency instabilities in the $10^{-16}$, competitive with the best international frequency standards available. However, a serious challenge inherent in compact clocks is the necessarily smaller optical beams, which results in rapid variation in interrogating wavefronts. This can cause inhomogeneous excitation of the thermal beam leading to long term drifts in the output frequency. Here we develop a model for Ramsey-Bord\'e interferometery using optical fields with curved wavefronts and simulate the $^{40}$Ca beam clock experiment described in [Olson et al., Phys. Rev. Lett. 123, 073202 (2019)]. Olson et al.'s results had shown surprising and unexplained behaviour in the response of the atoms in the interrogation. Our model predicts signals consistent with experimental data and can account for the significant sensitivity to laser geometry that was reported. We find the signal-to-noise ratio is maximised when the laser is uncollimated at the interrogation zones to minimise inhomogeneity, and also identify an optimal waist size determined by both laser inhomogeneity and the velocity distribution of the atomic beam. We investigate the shifts and stability of the clock frequency, showing that the Gouy phase is the primary source of frequency variations arising from laser geometry.Comment: 13 pages, 7 figure

Effect of surface roughness on metal enhanced fluorescence in planar substrates and optical fibers

Published 27 May 2016Abstract not availableElizaveta Klantsataya, Alexandre François, Heike Ebendorff-Heidepriem, Beniamino Sciacca, Agnieszka Zuber, and Tanya M. Monr

Exposed core microstructured optical fiber surface plasmon resonance biosensor

Surface Plasmon Resonance (SPR) scattering offers significant advantages compared to traditional reflectivity measurements, essentially turning a non-radiative process into a radiative one. Recently, we have shown that SPR scattering can be used in an optical fiber, enabling higher signal to noise ratio, reduced dependence on the metallic thickness as well as the unique capability of multiplexed detection with a single fiber. Here we report a novel SPR scattering based sensor fabricated based on an exposed-core silica Microstructured Optical Fiber (MOF). This MOF presents a structure with a relatively small core (Ø = 10μm), exposed along the whole fiber length. This exposed core MOF allows for fabrication of SPR supporting metallic thin films directly onto the fiber core offering the new prospect of exploiting SPR in a waveguide structure that supports only a relatively small number of guided optical modes, with a structure that offers ease of fabrication and handling. A thin silver film of 50 nm thickness was deposited onto the fiber core by thermal evaporation. The significant surface roughness of the prepared metallic coatings facilitates strong scattering of the light wave coupled into the surface plasmon. Performance characteristics of the new exposed core fiber sensor were compared to those of a large bare core silica fiber (Ø = 140μm). Although sensitivity of both sensors was comparable (around 2500nm/RIU), full width at half maximum (FWHM) of the SPR peaks for the new exposed core fiber sensor decreased by a factor of 3 offering an significant enhancement in the detection limit of the new sensing platform in addition to the prospect of a sensor with a lower detection volume.Elizaveta Klantsataya, Alexandre François, Agnieszka Zuber, Valeria Torok, Roman Kostecki and Tanya M. Monr

Impact of rare earth doping on the luminescence of lanthanum aluminum silicate glasses for radiation sensing

Large core soft glass fibers have been demonstrated to be promising candidates as intrinsic fiber sensors for radiation detection and dosimetry applications. Doping with rare earth ions enhanced their radiation sensitivity. SiO2-Al2O3-La2O3 (SAL) glasses offer easy fabrication of large core fibers with high rare earth concentration and higher mechanical strength than soft glasses. This paper evaluates the suitability of the SAL glass type for radiation dosimetry based on optically stimulated luminescence (OSL) via a comprehensive investigation of the spectroscopic and dosimetric properties of undoped and differently rare earth doped bulk SAL glass samples. Due to the low intensity of the rare earth luminescence peaks in the 250–400 nm OSL detection range, the OSL response for all the SAL glasses is not caused by the rare earth ions but by radiation-induced defects that act as intrinsic centers for the recombination of electrons and holes produced by the ionizing radiation, trapped in fabrication induced defect centers, and then released via stimulation with 470 nm light. The rare earth ions interfere with these processes involving intrinsic centers. This dosimetric behavior of highly rare earth doped SAL glasses suggests that enhancement of OSL response requires lower rare earth concentrations and/or longer wavelength OSL detection range

Refractometric micro-sensor using a mirrored capillary resonator

Published 17 Oct 2016We report on a flow-through optical sensor consisting of a microcapillary with mirrored channels. Illuminating the structure from the side results in a complicated spectral interference pattern due to the different cavities formed between the inner and outer capillary walls. Using a Fourier transform technique to isolate the desired channel modes and measure their resonance shift, we obtain a refractometric detection limit of (6.3 ± 1.1) x 10−6 RIU near a center wavelength of 600 nm. This simple device demonstrates experimental refractometric sensitivities up to (5.6 ± 0.2) x 102 nm/RIU in the visible spectrum, and it is calculated to reach 1540 nm/RIU with a detection limit of 2.3 x 10−6 RIU at a wavelength of 1.55 µm. These values are comparable to or exceed some of the best Fabry-Perot sensors reported to date. Furthermore, the device can function as a gas or liquid sensor or even as a pressure sensor owing to its high refractometric sensitivity and simple operation.William Morrish, Peter West, Nathan Orlando, Elizaveta Klantsataya, Kirsty Gardner, Stephen Lane, Raymond Decorby, Alexandre François, and Alkiviathes Meldru

Dual Laser Study of Non-Degenerate Two Wavelength Upconversion Demonstrated in Sensitizer-Free NaYF4:Pr Nanoparticles

Published online: February 1, 2021Understanding the upconversion pathways of a rare-earth dopant is crucial to furthering the use of that material, either toward applications in imaging or elsewhere. This work outlines a new analysis approach that consists of using two synchronized widely-tunable laser sources to explore the properties of upconverting materials. By examining sensitizer-free rare-earth nanoparticles based on a matrix of hexagonal sodium yttrium tetrafluoride (β-NaYF4) doped with praseodymium but no ytterbium sensitizer, a “non-degenerate” two-color upconversion fluorescence at a combined excitation of 1020–850 nm is shown. This insight demonstrates the ability of this technique to locate and interrogate novel upconversion pathways. The dopant level of the nanoparticles could be modified without altering other factors, such as the particle's shape or size, that would also change optical properties and this allows investigation of the dopant-level dependency of the optical properties. The approach also allows exploration of the time delay domain between the arrival times of the two non-degenerate excitation pulses, which allows modulation of the brightness from the visible light emissions. This work opens up the parameter space for the systematic synthesis and characterization of new materials with non-degenerate upconversion emission.Thomas J. de Prinse, Afshin Karami, Jillian E. Moffatt, Thomas B. Payten, Georgios Tsiminis, Lewis Da Silva Teixeira, Jingxiu Bi, Tak W. Kee, Elizaveta Klantsataya, Christopher J. Sumby, and Nigel A. Spoone

Impact of rare earth doping on the luminescence of lanthanum aluminum silicate glasses for radiation sensing

Large core soft glass fibers have been demonstrated to be promising candidates as intrinsic fiber sensors for radiation detection and dosimetry applications. Doping with rare earth ions enhanced their radiation sensitivity. SiO2-Al2O3-La2O3 (SAL) glasses offer easy fabrication of large core fibers with high rare earth concentration and higher mechanical strength than soft glasses. This paper evaluates the suitability of the SAL glass type for radiation dosimetry based on optically stimulated luminescence (OSL) via a comprehensive investigation of the spectroscopic and dosimetric properties of undoped and differently rare earth doped bulk SAL glass samples. Due to the low intensity of the rare earth luminescence peaks in the 250–400 nm OSL detection range, the OSL response for all the SAL glasses is not caused by the rare earth ions but by radiation-induced defects that act as intrinsic centers for the recombination of electrons and holes produced by the ionizing radiation, trapped in fabrication induced defect centers, and then released via stimulation with 470 nm light. The rare earth ions interfere with these processes involving intrinsic centers. This dosimetric behavior of highly rare earth doped SAL glasses suggests that enhancement of OSL response requires lower rare earth concentrations and/or longer wavelength OSL detection range.Ruth E. Shaw, Christopher A. G. Kalnins, Carly A. Whittaker, Jillian E. Moffatt, Georgios Tsiminis, Elizaveta Klantsataya, David Ottaway, Nigel A. Spooner, Doris Litzkendorf, Anne Matthes, Anka Schwuchow, Katrin Wondraczek, and Heike Ebendorff-Heideprie